1. Field of the Invention
The invention relates to a television tuner switching a mode between UHF and VHF modes to thereby receive signals having frequencies of UHF and VHF bands, a tuner integrated circuit (IC) for controlling operation modes of such a television tuner, and a method of controlling a television tuner.
2. Description of the Related Art
In general, three frequency bands are now utilized as radio wave for television broadcasting: Very High Frequency-Low (VHF-L) band; Very High Frequency-High (VHF-H) band; and Ultra High Frequency (UHF) band.
A so-called television tuner has conventionally selected a channel by means of a logical channel (LC) tuning circuit. However, it is quite difficult to cover the above-mentioned three bands by a single LC tuning circuit. Hence, a conventional television tuner has been designed to include three LC tuning circuits each associated with the above-mentioned three bands, which LC tuning circuits are alternately switched. This is the same in a LC oscillation circuit of a frequency converter.
In the United States, a frequency band for FM radio broadcasting is positioned between VHF-L and VHF-H bands for television broadcasting. Hence, when radio waves for television broadcasting in VHF-L and VHF-H bands are to be received, radio waves for radio broadcasting in FM band may interfere with them to thereby degrade images and/or sound in quality. In order to avoid such interference, it would be necessary to trap radio waves for radio broadcasting in FM band.
In cable television service now spreading in the United States, a frequency band of signals for cable television is almost the same as a frequency band of signals for radio wave for television broadcasting, but is assigned FM band used for radio broadcasting. Hence, when a cable television is in operation, it is impossible to trap FM band.
Hence, in a television tuner available in the United States, a FM trap circuit for trapping signals of FM band is connected to an antenna through which radio waves for television broadcasting are received. The FM trap circuit is operated when radio waves for television broadcasting in VHF-L and VHF-H bands are to be received, and is paused when signals of a cable television are to be received through a cable.
A television tuner now available is not designed to switch only a LC tuning circuit in order to switch signals to be received between VHF-L and VHF-H bands, and UHF band. Circuits for amplifying high frequency and circuits for converting frequency separately prepared for VHF-L and VHF-H bands, and UHF band are connected to a front stage of a LC tuning circuit to thereby define a circuit for receiving signals having a frequency of VHF-L and VHF-H bands, and a circuit for receiving signals having a frequency of UHF band. The thus defined circuits are wholly, selectively switched.
The television tuner having such a structure as mentioned above makes it possible to simplify a circuit structure thereof, suppress degradation in characteristics, and optimize noise figure (NF) and operation current of transistors constituting the circuit, in accordance with a band. The above-mentioned control for switching circuits for receiving signals having frequencies of VHF-L and -H bands, and UHF band is generally carried out by means of operation switching signals standardized by a micro-computer, using an integrated injection logic (IIL) gate as standard specification.
An example of conventional television tuners is explained hereinbelow with reference to FIGS. 1, 2A and 2B, wherein FIG. 1 is a block diagram of a television tuner, FIG. 2A is a partial block diagram of a tuner integrated circuit, and FIG. 2B illustrates data for switching a band.
As illustrated in FIG. 1, the illustrated television tuner 1 is comprised of a high frequency amplifying section 100, a tuner integrated circuit 200, a logical channel (LC) section 300, and a control circuit 400.
The high frequency amplifying section 100 amplifies signals for radio wave or cable television broadcasting. The tuner IC 200 converts the amplified television signals into an intermediate frequency. The control circuit 400 is comprised of a microcomputer in which a suitable control program is installed as software, and controls operation of the high frequency amplifying section 100 and the tuner IC 200.
The tuner IC 200 includes a frequency converter 2 to which a tuner controller 3 is connected. The high frequency amplifying section 100 includes a first amplifier 4 for amplifying a frequency of UHF band, and a second amplifier 5 for amplifying frequencies of VHF-L and -H bands. The first and second amplifiers 4 and 5 are connected upstream to the frequency converter 2. A FM trap circuit 6 is connected upstream to the second amplifier 5.
The FM trap circuit 6 to which the second amplifier 5 is connected, and the first amplifier 4 are both connected to a switch device 7, to which an antenna (not illustrated) for receiving radio wave broadcasting or a communication cable (not illustrated) for cable broadcasting is connected through an input terminal 8.
The frequency converter 2 includes a first frequency mixer 11 for UHF band and a second frequency mixer 12 for VHF-L and -H bands, which are connected to a first local oscillator (LO) 13 for UHF band and a second local oscillator (LO) 14 for VHF-L and -H bands, respectively.
The first and second local oscillators 13 and 14 are connected to a phase locked loop (PLL) section 15 through a buffer amplifier 19. The phase locked loop section 15 is connected to the first and second local oscillators 13 and 14 for feedback through logical channels 16 and 17 for UHF band, and VHF-L and -H bands, respectively, in the logical channel section 300.
As mentioned above, the first and second amplifiers 4 and 5, the first and second mixers 11 and 12, the first and second local oscillators 13 and 14, and the first and second logical channels 16 and 17 are equipped separately for UHF band, and VHF-L and -H bands, and are connected in series to thereby define a first circuit 500 for receiving signals having a frequency of UHF band, and a second circuit 600 for receiving signals having a frequency of VHF-L and -H bands.
The first and second local oscillators 13 and 14 oscillate at certain frequencies. The first and second mixers 11 and 12 convert frequencies of television signals in UHF band and VHF-L and -H bands into intermediate frequencies by mixing them with frequencies of oscillation made by the first and second local oscillators 13 and 14. The phase locked loop section 15 outputs a control voltage to the first and second logical channels 16 and 17 in accordance with the oscillation frequencies of the first and second local oscillators 13 and 14, respectively, and cooperates with the first and second logical channels 16 and 17 to control oscillation frequencies of the first and second local oscillators 13 and 14 by feed-back.
As illustrated in FIG. 1, the phase locked loop section 15 is comprised of a frequency divider 41, a phase detector 42, a standard oscillator 43, a charge pump 44, and a buffer amplifier 45. The frequency divider 41 divides a local oscillation signal transmitted from the buffer amplifier 19. The standard oscillator 43 transmits an oscillation signal having a certain frequency.
The phase detector 42 generates a voltage proportional to a difference in phase between a frequency division signal transmitted by the frequency divider 41 and the oscillation signal transmitted from the standard oscillator 43.
The charge pump 44 increases an output voltage of the phase detector 42 up to a certain voltage. The buffer amplifier 45 removes high frequency parts out of the thus increased voltage, and outputs the resultant voltage to the first and second logical channels 16 and 17 as a control voltage.
The frequency divider 41 can vary a division ratio in accordance with a signal transmitted from the control circuit 400 in order to conform to a received channel. Hence, an output signal transmitted from the frequency divider 41 has a certain frequency regardless of a frequency of a received signal.
The standard oscillator 43 can vary its oscillation frequency in accordance with the control signal transmitted from the control circuit 400 in order to conform to a band and/or channel interval of various areas.
An UV switching buffer 18 is connected to the first and second mixers 11 and 12, and is connected further to a tuner control section 3. The tuner control section 3 includes a band switching buffer 21 which is provided with output terminals P1, P2, P3, and P4 arranged in a row in this order. Control signals for VHF-L band, VHF-H band, FM band, and UHF band are transmitted through the output terminals P1, P2, P3, and P4.
The output terminal for UHF band is connected to the first amplifier 4 used for UHF band. The output terminals P1 and P2 for VHF-L and VHF-H bands, respectively, are both connected to the second amplifier used for VHF-L and VHF-H bands. The output terminal P4 for UHF band is connected not only to the first amplifier 4, but also to the UV switching buffer 18.
The band switching buffer 21 is connected to a data converter 22, to which the phase locked loop section 15 and the control circuit 400 are connected. More specifically, as illustrated in FIG. 2A, the control circuit 400 is connected to the data converter 22 through an IIC bus 23 including a data input wiring 24 and a clock input wiring 25. These input wirings 24 and 25 are connected to a serial-parallel converter 26 of the data converter 22.
The serial-parallel converter 26 is comprised of eight D-type flip-flop circuits 27 to 35 which are electrically connected in serial to each other so that an input terminal of a flip-flop circuit located upstream is connected to a normal output terminal of a flip-flop circuit located downstream. Normal output terminals of the first four flip-flop circuits 27, 28, 29 and 30 of the serial-parallel converter 26 are connected in parallel to input terminals of the remaining four flip-flop circuits 32, 33, 34, and 35 constituting a data latch circuit 31. A 8-clock counter 36 connected to the clock input wiring 25 is connected to controls terminals of the four flip-flop circuits 32, 33, 34, and 35 constituting the data latch circuit 31.
Normal output terminals of the four flip-flop circuits 32, 33, 34, and 35 are connected in parallel to a four-bit band switching buffer 37. Four bit buffers equipped with the band switching buffer 37 are connected to the output terminals P1, P2, P3 and P4 through which the control signals for UHF band, FM band, VHF-H band, and VHF-L band are transmitted.
Though detailed later, 8-bit operation switching signals by each of which indicates as one-bit data that VHF-L band, VHF-H band, UHF band, or none of them is selected are input in serial to the serial-parallel converter 26 of the tuner controller 3 from the control circuit 400. The band switching buffer 37 of the tuner controller 3 transmits at least four-bit operation switching signals in parallel by each of which indicates as one-bit data that VHF-L band, VHF-H band, UHF band, or none of them is selected.
As illustrated in FIG. 2A, the band switching buffer 37 includes first, second, third and fourth bit buffers B1, B2, B3, and B4. The first and second bit buffers B1 and B2 retaining setting data D1 and D2 about VHF-L band and VHF-H band, respectively, are connected to the second amplifier 5 used for VHF-L and VHF-H bands. The third bit buffer B3 retaining setting data D3 about FM band is connected to the FM trap circuit 6. The fourth bit buffer B4 retaining setting data D4 about UHF band is connected to the first amplifier 4 used for UHF band, and further to the UV switching buffer 18 of the frequency converter 2 through a control output wiring 38.
The first and second bit buffers B1 and B2 of the band switching buffer 37 are connected further to the second amplifier used for VHF-L and -H bands. The fourth bit buffer B4 is connected to the first amplifier 4, and further to the second amplifier 5 through an inverter. That is, one of the first and second amplifiers 4 and 5 operates in accordance with whether the setting data D4 about UHF band is selected or not. The second amplifier 5 used for VHF-L and -H bands switches tuning frequency band of a built-in LC tuning circuit (not illustrated) between VHF-L band and VHF-H band in accordance with the setting data D1 and D2 about VHF-L band and VHF-H band, respectively.
The television tuner 1 having the above-mentioned structure is used for receiving television radio waves in the United States, for instance. In the United States, since FM band of radio waves used for radio broadcasting is assigned between VHF-H and VHF-L bands, it is necessary to trap FM band in order to avoid interference when radio waves in VHF-H and -L bands are to be received.
On the other hand, a frequency band for transmission signals of a cable television is almost the same as the above-mentioned frequency band of a television ground wave. However, since a channel of the frequency band for transmission signals of a cable television is assigned also to FM band, it is not possible to trap FM band when cable television signals are to be received. Hence, the television tuner 1 turns on the FM trap circuit 6 for trapping FM band or turns off the FM trap circuit 6 for pausing to trap FM band by the tuner controller 3 in accordance with whether radio waves in VHF-L and -H bands or cable signals of a cable television are received.
The above-mentioned radio waves for television broadcasting and wired signals for a cable television cover from VHF-L and -H bands to UHF band. For this reason, it is quite difficult to use a hardware for both UHF band, and VHF-L and -H bands. Specifically, the frequency converter 2 can receive signals having frequency ranging from UHF band to VHF-L and -H bands. However, since it is necessary to switch operation modes for receiving signals in UHF band and VHF-L and -H bands, the tuner controller 3 carries out such switching.
In more detail, as illustrated in FIG. 2B, 8-bit operation switching signals including data "X, X, X, X, U, FM, VH, VL" (indicates any data) each of which indicates VHF-L band, VHF-H band, FM band, UHF band, or none of them is selected, are input in serial in this order to the data input wiring 24 of the tuner controller 3 from the control circuit 400.
Since the operation switching signals are serially input to the data input wiring 24 in synchronization with clock signals, at a time when an eighth clock signal has been input, the last four-bit data "U, FM, VH, VL" in the 8-bit operation switching signals is retained in the first to fourth flip-flop circuits 27 to 30 of the serial-parallel converter 26, respectively.
When the eighth clock signal has been input to the data input wiring 24 as mentioned earlier, the 8-clock counter 36 which repeats counting clock signals transmits a latch signal to the data latch circuit 31. Hence, the last four-bit data "U, FM, VH, VL" in the 8-bit operation switching signals, retained in the flip-flop circuits 27 to 30, are transferred in parallel to the four flip-flop circuits 32 to 35 of the data latch circuit 31, and retained therein.
The four-bit operation switching signals converted into parallel data are individually retained in the flip-flop circuits 32 to 35 of the data latch circuit 31, and then, input in parallel to the four bit buffers B1, B2, B3 and B4 of the band switching buffer 37. The parallel four-bit operation switching signals transmitted to the band switching buffer 37 indicates in each bit whether VHF-H band, VHF-L band, FM band, or UHF band is selected.
For instance, if UHF band is selected as a band for receiving signals, only the setting data for UHF band is set to be "1", and other setting data for VHF-H, VHF-L and FM bands are set to be "0". The band switching buffer 37 transmits control signals to the frequency converter 2 through the control output wiring 38 in accordance with the setting data for UHF band which is input to the fourth bit buffer B4.
The frequency converter 2 receives the control signals, as mentioned above. The UV switching buffer 18 switches the first and second mixers 11 and 12, and the first and second local oscillators 13 and 14 in accordance with the control signals input thereto. As a result, an operation mode of the television tuner 1 is switched between VHF mode used for receiving signals having a frequency in VHF-L and -H bands, and UHF mode used for receiving signals having a frequency in UHF band.
As mentioned above, there are generated the operation switching signals for both VHF-L and -H bands for the purpose of switching a tuning frequency of the second amplifier to be used for VHF-L and -H bands. However, since switching between VHF and UHF modes is carried out in accordance with whether the setting data about UHF band indicates that UHF band is selected, VHF mode can be selected regardless of which one of the setting data about VHF-H and -L bands is selected.
The setting data about FM band is inevitably selected only when wired signals for a cable television are to be received, and is not selected when radio waves for television broadcasting are to be received. Hence, the FM trap circuit 6 to which the setting data about FM band is transmitted as a control signal from the band switching buffer 21 is designed not to trap FM band when the setting data about FM band indicates that FM band is selected, but trap FM band when the setting data indicates that FM band is not selected.
Thus, since FM band is trapped when radio waves for television broadcasting are received, radio waves in VHF-L and -H bands adjacent to FM band are well received by the second circuit 600. In addition, since FM band is not trapped when wired signals for a cable television are received, wired signals in FM band can be well received by the second circuit 600.
As the tuner IC 200 operating in such a manner as mentioned above, there may be employed TDA 6402A commercially available from Philips Ltd. (Philips data sheet, TDA 6402A, TDA 6403, TDA 6403A, Mar. 6, 1997).
In the above-mentioned television tuner 1, since the tuner controller 3 switches operation modes of the frequency converter 2 in accordance with the operation switching signals transmitted from the control circuit 400, the frequency converter 2 can receive UHF and VHF signals.
However, some television tuners are designed to have a different arrangement of the first and second amplifiers 4 and 5, and the FM trap circuit 6 from the arrangement of those in the television tuner 1 illustrated in FIG. 1. In such television tuners, data wirings connecting the band switching buffer 37 to the frequency converter 2 intersect with each other.
Data wirings for a television tuner are generally patterned on a printed wiring board. In order to intersect data wirings with each other as mentioned above, it would be necessary to form a wiring pattern in a multi-layered structure, or make jumper wirings, either of which would significantly lower a fabrication yield of a television tuner.
Hence, in order to avoid intersection of data wirings, a television tuner having such a layout as mentioned above changes an order of setting data about UHF and FM bands in the operation switching signals. As a result, the control signals are transmitted from the tuner controller 3 to the frequency converter 2 in accordance with the setting data about FM band in the operation switching signals.
For instance, when the frequency converter 2 and the tuner controller 3 are constituted of separate parts, what is necessary to do is merely to adjust a wiring structure. However, when the frequency converter 2 and the tuner controller 3 are constituted of the single tuner IC 200, it is quite difficult to adjust a wiring structure in accordance with a format of the operation switching signals.
In order to solve such a problem, there has been suggested a tuner IC which can conform to the above-mentioned format of the operation switching signals. FIG. 3 illustrates such a tuner IC 700. In the illustrated tuner IC 700, the third bit buffer B3 of the band switching buffer 37 is directly connected to the UV switching buffer 18 through the control output wiring 38. As a tuner IC having such a structure as illustrated in FIG. 3, there is TDA 6402 commercially available from Philips Ltd.
That is, there has been used two kinds of formats of the operation switching signals to conform to two layouts of television tuners. As a result, there has been prepared two kinds of tuner ICs in accordance with the two kinds of the operation switching signals. Specifically, there has been prepared TDA 6402 and TDA 6402A both of which are commercially available from Philips Ltd., as the tuner ICs 200 and 700, respectively.
As a result, fabrication yields for the tuner ICs 200 and 700 have remained low, and in addition, the number of fabrication steps and load on stock control has been increased. The above-mentioned two kinds of tuner ICs such as the tuner ICs 200 and 700 are generally designed to have the same appearance in order to keep compatibility in a mold for making a resin package and/or in a shape of a connector, which is accompanied with a problem that the tuner IC 200 or 700 may be incorporated into an inappropriate television tuner.